The present invention is directed to the production of anhydrous hydrofluoric acid.
Commercial grade hydrofluoric acid is generally prepared by the reaction of acid-grade (high purity) fluorspar with strong sulfuric acid, and sometimes oleum, in a specially designed reactor. To produce anhydrous hydrofluoric acid, the fluorspar must first be dried completely. Hot, dry gas is sparged through the reaction mass during the reaction to maintain the temperature and drive off the hydrogen fluoride. The hydrogen fluoride gas is then condensed or scrubbed. The calcium sulfate remaining in the reactor contains excess sulfuric acid, which must be neutralized before disposal.
U.S. Pat. Nos. 1,316,569; 2,088,048; 2,846,290; 2,932,557; 3,102,787; 3,160,473; 3,300,279; 3,469,939; 3,718,736; 3,725,536; 3,825,655; 3,878,294; 4,010,245; and 4,120,939 each disclose processes for the production of hydrofluoric acid by the reaction of fluorspar and sulfuric acid. U.S. Pat. No. 4,268,492 discloses a process for the production of an alkali metal sulfate and hydrofluoric acid from sulfuric acid and an alkali metal fluosilicate, with the patent also disclosing that hydrogen fluoride and SiF.sub.4 (H.sub.2 SiF.sub.6) may be reacted with an alkali metal chloride to produce hydrochloric acid and an alkali metal fluosilicate.
It would, however, be desirable to provide an economical process for the production of anhydrous hydrofluoric acid by use of low grade sources of fluorine which process avoids the need for time-consuming and expensive treatment of the fluorine-containing raw material.